Would my son be entitled?

my son had moved back home due to illness. he has been awarded dla middle care component and low mobility rate. He also gets income support with a disability premium, now dss have witten to him saying he would be entitled to something called severe disability premium if no one claims carers allowance for him (which they dont). but i was wondering can he still claim this as he is living with me. i am also on incapacity benefit and receive housing benefit.